Process for producing perforated film

Abstract

A process for the manufacture of thermoplastic sheet having elliptical perforations including a rotatable molding element having a series of hexagonal-shaped depressions having centered therein elliptical holes, the elliptical holes having a major axis and a minor axis, the major axis being oriented parallel to the direction in which the molding element is rotated, a means for applying a fluid pressure differential to a surface of the thermoplastic sheet to force the sheet against the molding element to effect rupturing of the sheet and the formation of elliptical holes in the sheet.

What is claimed is: 
     
       1. A process for the manufacture of thermoplastic sheet having elliptical perforations comprising: a. placing a thermoplastic sheet into contact with a continuously rotating molding element means having hexagonal-shaped depression means in which a series of elliptical hole means are centered, said hole means having a major axis and a minor axis, said major axis being oriented parallel to the direction in which said molding element means is rotating;   b. subjecting a surface of said thermoplastic sheet to the action of a fluid pressure differential to cause said sheet to flow into said elliptical hole means while maintaining said pressure differential to effect rupturing of said thermoplastic sheet and the formation of elliptical hole means in said sheet; and,   c. continuously removing the molded portions of said sheet from said molding element means.   
     
     
       2. The process of claim 1 wherein said thermoplastic sheet is heated to soften said sheet prior to said sheet coming into contact with said continuously rotating molding element means. 
     
     
       3. The process of claim 1 wherein said sheet means is cooled prior to removing said molded portions from said molding element means. 
     
     
       4. The process of claim 1 wherein said major axis has a length of from about 24 mils to about 26 mils and said minor axis has a length of from about 17 mils to about 19 mils. 
     
     
       5. The process of claim 1 wherein said major axis has a length of about 25 mils and said minor axis has a length of about 18 mils.